Provided are a stack chip and a stack chip package having the stack chip. Internal circuits of two semiconductor chips are electrically connected to each other through an input/output buffer connected to an external connection terminal. The semiconductor chip has chip pads, input/output buffers and internal circuits connected through circuit wirings. The semiconductor chip also has connection pads connected to the circuit wirings connecting the input/output buffers to the internal circuits. The semiconductor chips include a first chip and a second chip. The connection pads of the first chip are electrically connected to the connection pads of the second chip through electrical connection means. Input signals input through the external connection terminals are input to the internal circuits of the first chip or the second chip via the chip pads and the input/output buffers of the first chip, and the connection pads of the first chip and the second chip.